Chapter 7

Information Storage and
Management
Storing, Managing, and Protecting Digital Information
Ali Broumandnia, Broumandnia@gmail.com 1

Section II Storage Networking
Technologies and Virtualization
In This Section:
• Chapter 5: Direct-Attached Storage and Introduction to SCSI
• Chapter 6: Storage Area Networks
• Chapter 7: Network-Attached Storage
• Chapter 8: IP SAN

Chapter 7
Network-Attached Storage
• 7.1 General-Purpose Servers vs. NAS Devices
• 7.2 Benefits of NAS
• 7.3 NAS File I/O
• 7.4 Components of NAS
• 7.5 NAS Implementations
• 7.6 NAS File-Sharing Protocols
• 7.7 NAS I/O Operations
• 7.8 Factors Affecting NAS Performance and Availability
• 7.9 Concepts in Practice: EMC Celerra
• SummaryAli Broumandnia, Broumandnia@gmail.com 3

Key Concepts:
• NAS Device
• Remote File Sharing
• NAS Connectivity and Protocols
• NAS Performance and Availability
• MTU and Jumbo Frames

This chapter describes the components of NAS, different
types of NAS implementations, the file-sharing
protocols, and the transport and network layer protocols
used in NAS implementations. The chapter also explains
NAS design considerations and factors that affect NAS
performance.

7.1 General-Purpose Servers vs. NAS
Devices
A NAS device is optimized for file-serving functions such
as storing, retrieving, and accessing files for applications
and clients. As shown in Figure 7-1, a general-purpose
server can be used to host any application, as it runs a
generic operating system. Unlike a general-purpose server,
a NAS device is dedicated to file-serving.

7.2 Benefits of NAS
 Supports comprehensive access to information
 Improved efficiency
 Improved flexibility
 Centralized storage
 Simplified management
 Scalability
 High availability
 Security

7.3 NAS File I/O
NAS uses file-level access for all of its I/O operations.
File I/O is a high-level request that specifies the file to be
accessed, but does not specify its logical block address.
For example, a file I/O request from a client may specify
reading 256 bytes from byte number 1152 onward in a
specific file. Unlike block I/O, there is no disk volume or
disk sector information in a file I/O request. The NAS
operating system keeps track of the location of files on
the disk volume and converts client file I/O into block-
level I/O to retrieve data.

7.3.1 File Systems and Remote File
Sharing
A file system is a structured way of storing and
organizing data files. Many file systems maintain a file
access table to simplify the process of finding and
accessing files.

7.3.2 Accessing a File System
A file system must be mounted before it can be used. In
most cases, the operating system mounts a local file
system during the boot process. The mount process
creates a link between the file system and the operating
system. When mounting a file system, the operating
system organizes files and directories in a tree-like
structure and grants the user the privilege of accessing
this structure.

The tree is rooted at a mount point that is named using
operating system conventions. Users and applications
can traverse the entire tree from the root to the leaf
nodes. Files are located at leaf nodes, and directories and
subdirectories are located at intermediate roots. The
relationship between the user and the file system
terminates when the file system is unmounted. Figure 7-2
shows an example of the UNIX directory structure under
UNIX operating environments.

7.3.3 File Sharing
File Transfer Protocol (FTP), distributed file systems,
and a client/server model that uses a file-sharing protocol
are some examples of implementations of file-sharing
environments. A distributed file system (DFS) is a file
system that is distributed across several hosts. A DFS can
provide hosts with direct access to the entire file system,
while ensuring efficient management and data security.

7.4 Components of NAS
• NAS head (CPU and Memory)
• One or more network interface cards (NICs), which
provide connectivity to the network. Examples of NICs
include Gigabit Ethernet, Fast Ethernet, ATM, and
Fiber Distributed Data Interface (FDDI).
• An optimized operating system for managing NAS
functionality

• NFS and CIFS protocols for file sharing
• Industry-standard storage protocols to connect and
manage physical disk resources, such as ATA, SCSI, or
FC
The NAS environment includes clients accessing a NAS
device over an IP network using standard protocols.

7.5 NAS Implementations
As mentioned earlier, there are two types of NAS
implementations: integrated and gateway. The integrated
NAS device has all of its components and storage system
in a single enclosure. In gateway implementation, NAS
head shares its storage with SAN environment.

7.5.1 Integrated NAS
An integrated NAS device has all the components of
NAS, such as the NAS head and storage, in a single
enclosure, or frame. This makes the integrated NAS a
self-contained environment. The NAS head connects to
the IP network to provide connectivity to the clients and
service the file I/O requests. The storage consists of a
number of disks that can range from low-cost ATA to
high throughput FC disk drives. Management software
manages the NAS head and storage configurations.

7.5.2 Gateway NAS
A gateway NAS device consists of an independent NAS
head and one or more storage arrays. The NAS head
performs the same functions that it does in the integrated
solution; while the storage is shared with other
applications that require block-level I/O. Management
functions in this type of solution are more complex than
those in an integrated environment because there are
separate administrative tasks for the NAS head and the
storage.

7.5.3 Integrated NAS Connectivity
An integrated solution is self-contained and can connect
into a standard IP network. Although the specifics of how
devices are connected within a NAS implementation
vary by vendor and model. In some cases, storage is
embedded within a NAS device and is connected to the
NAS head through internal connections, such as ATA or
SCSI controllers. In others, the storage may be external
but connected by using SCSI controllers.

In a high-end integrated NAS model, external storage
can be directly connected by FC HBAs or by dedicated
FC switches. In the case of a low-end integrated NAS
model, backup traffic is shared on the same public IP
network along with the regular client access traffic. In
the case of a high-end integrated NAS model, an isolated
backup network can be used to segment the traffic from
impeding client access.

More complex solutions may include an intelligent
storage subsystem, enabling faster backup and larger
capacities while simultaneously enhancing performance.
Figure 7-4 illustrates an example of integrated NAS
connectivity.

7.5.4 Gateway NAS Connectivity
In a gateway solution, front-end connectivity is similar to
that in an integrated solution. An integrated environment
has a fixed number of NAS heads, making it relatively
easy to determine IP networking requirements. In
contrast, networking requirements in a gateway
environment are complex to determine due to scalability
options. Adding more NAS heads may require additional
networking connectivity and bandwidth.

Communication between the NAS gateway and the
storage system in a gateway solution is achieved through
a traditional FC SAN. To deploy a stable NAS solution,
factors such as multiple paths for data, redundant fabrics,
and load distribution must be considered. Figure 7-5
illustrates an example of gateway NAS connectivity.

7.6 NAS File-Sharing Protocols
Most NAS devices support multiple file service protocols
to handle file I/O requests to a remote file system. As
mentioned earlier, NFS and CIFS are the common
protocols for file sharing. NFS is predominantly used in
UNIX-based operating environments; CIFS is used in
Microsoft Windows–based operating environments.
These file sharing protocols enable users to share file
data across different operating environments and provide
a means for users to migrate transparently from one
operating system to another.

7.6.1 NFS
oSearching files and directories
oOpening, reading, writing to, and closing a file
oChanging file attributes
oModifying file links and directories

NFS version 2 (NFSv2): Uses UDP to provide a
stateless network connection between a client and a
server. Features such as locking are handled outside the
protocol.
NFS version 3 (NFSv3): The most commonly used
version, it uses UDP or TCP, and is based on the
stateless protocol design. It includes some new
features, such as a 64-bit file size, asynchronous writes,
and additional file attributes to reduce re-fetching.

NFS version 4 (NFSv4): This version uses TCP and is
based on a state full protocol design. It offers enhanced
security.

7.6.2 CIFS
CIFS is a client/server application protocol that enables
client programs to make requests for files and services on
remote computers over TCP/IP. It is a public, or open,
variation of Server Message Block (SMB) protocol. The
CIFS protocol enables remote clients to gain access to
files that are on a server. CIFS enables file sharing with
other clients by using special locks.

File names in CIFS are encoded using Unicode characters.
CIFS provides the following features to ensure data integrity:
It uses file and record locking to prevent users from
overwriting the work of another user on a file or a record.
It runs over TCP.
It supports fault tolerance and can automatically
restore connections and reopen files that were open
prior to interruption.

7.7 NAS I/O Operations
The NFS and CIFS protocols handle file I/O requests to a
remote file system, which is managed by the NAS
device. The process of NAS I/O is as follows:

1. The requestor packages an I/O request into TCP/IP and forwards
it through the network stack. The NAS device receives this
request from the network.
2. The NAS device converts the I/O request into an appropriate
physical storage request, which is a block-level I/O, and then
performs the operation against the physical storage pool.
3. When the data is returned from the physical storage pool, the
NAS device processes and repackages the data into an
appropriate file protocol response.
4. The NAS device packages this response into TCP/IP again and
forwards it to the client through the network.

7.7.1 Hosting and Accessing Files on
NAS
1. Create storage array volumes
2. Create NAS Volumes
3. Create NAS file systems
4. Mount file systems
5. Access the file systems

7.8 Factors Affecting NAS Performance
and Availability
Network congestion is one of the most significant sources
of latency (Figure 7-7) in a NAS environment.

1. Number of hops
2. Authentication with a directory service such as
LDAP, Active Directory, or NIS
3. Retransmission
4. Over utilized routers and switches
5. File/directory lookup and metadata requests
6. Over utilized NAS devices
7. Over utilized clientsAli Broumandnia, Broumandnia@gmail.com 39

7.9 Concepts in Practice: EMC Celerra
EMC offers NAS solutions with the Celerra family of
products. Celerra is available in either a gateway or an
integrated configuration. EMC Celerra provides a
dedicated, high-performance, high-speed communication
infrastructure for file level I/O s. It uses a significantly
streamlined or tuned operating system. It supports
Network Data Management Protocol (NDMP) for
backup, CIFS, NFS, FTP, and iSCSI.

7.9.1 Architecture
Celerra consists of a Control Station and NAS heads
(Data Movers). The Data Mover is a network and storage
interface device and the control station is a management
interface device.

Data Mover
The Data Mover is an independent, autonomous file
server that transfers requested files to clients. Figure 7-8
shows the NS40 and NSX blade Data Movers. Data
Access in Real Time (DART) is Celerra’s specialized
operating system, which runs on the Data Mover. This
operating system is optimized for performing file
operations to move data from the storage array to the
network. DART supports standard network file access
protocols, such as NFS, CIFS, and FTP. Features of the
Celerra Data Mover include the following:Ali Broumandnia, Broumandnia@gmail.com 43

 Dual Intel processors
 PCI or PCI-X support
 High-memory capacity
 Multiport network cards
 Fibre Channel connectivity to storage arrays
 A highly specialized operating system (DART)

Control Station
The control station provides dedicated processing
capabilities to control, manage, and configure a NAS
solution. The control station hosts the Linux operating
system that is used to install, manage, and configure Data
Movers and monitor the environmental conditions and
performance of all components. The control station also
provides high-availability features such as fault
monitoring, fault recovery, fault reporting, call home,
and remote diagnostics.

Storage Connectivity
Celerra data movers connect to storage in two ways:
integrated and gateway. In the integrated configuration,
dedicated storage is assigned to Celerra (see Figure 7-9[a]).
In this configuration, the control station is connected to the
Data Movers via a private, internal IP network.

7.9.2 Celerra Product Family
NS Series: Integrated
• NS20
• NS40
NS Series: Gateway
• NS40G
• NSX

7.9.3 Celerra Management Software
• CLI Management : This can be accessed from the
control station through the SSH (secure shell) interface
tool, or PUTTY.
• GUI Management—Celerra Manager : GUI
management through the Celerra Manager has the
following two options—Celerra Manager Basic
Edition, or Celerra Manager Advanced Edition, which
is licensed separately and provides advanced features.

Summary
Decisions regarding storage infrastructure are based on
maintaining the balance between cost and performance.
Organizations look for the performance and scalability of
SAN combined with the ease of use and lower total cost
of ownership of NAS solutions. The convergence of
SAN and NAS is inevitable because of advances in
storage networking technology. Both SAN and NAS
have enjoyed unique advantages in enterprises, and the
advances in IP technology have scaled NAS solutions to
meet the demands of performance-sensitive applications.Ali Broumandnia, Broumandnia@gmail.com 51

Cost and ease of use drive the application’s needs in
terms of performance and capacity. Although NAS
invariably imposes higher protocol overhead, NAS
applications tend to be most efficient for file-sharing
tasks, such as NFS in UNIX, and CIFS in Microsoft
Windows. Network-based locking at the file level
provides a high level of concurrent access protection.

NAS can also be optimized to deliver file information to
many clients with file-level protection. Two common
applications that utilize the effectiveness of NAS include
hosting home directories and providing a data store for
static Web pages that are accessed by different Web
servers. In certain situations, organizations can deploy
NAS solutions for database applications in a limited
manner.

These situations are usually limited to applications for
which the majority of data access is read-only, the
databases are small, access volume is low, and
predictable performance is not mandatory. In this type of
situation, NAS solutions can reduce overall storage costs.

Careful evaluation of emerging trends in the networking
and storage industry is imperative when selecting the
appropriate technology. Along with the need for high
performance, ease of management and sharing of data
are also increasing. The choice of technology should
balance these requirements; consider the complexity and
maturity of the technology that is deployed. IP-SAN,
detailed in the following chapter, is an emerging
technology that has matured to meet enterprise demands.

Chapter 7

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